1. Field of the Invention
The present invention relates to an air conditioner for cooling or heating air in a room and a method for controlling an electronic expansion valve of the air conditioner.
2. Description of the Related Art
Generally, an air conditioner is an appliance for cooling or heating an indoor space, such as a residential space, a restaurant, an office, or etc. The air conditioner comprises a compressor for compressing a refrigerant into a high-temperature and high-pressure gaseous state, a condenser for condensing the refrigerant passing through the compressor into a high-temperature and high-pressure liquid state, an expansion device for decompressing the refrigerant passing through the condenser into a low-temperature and low-pressure liquid state, and an evaporator for evaporating the refrigerant passing through the expansion device into a low-temperature and low-pressure gaseous state. The compressor, the condenser, the expansion device, and the evaporator are connected by a refrigerant pipe. The operation of such an air conditioner is controlled by a microcomputer.
A heat pump system-type air conditioner further comprises a direction change valve, such as a 3-way valve or a 4-way valve, adapted to change the flow direction of the refrigerant based on a cooling/heating function, thereby being selectively operated in a cooling or heating mode.
In the cooling mode of the air conditioner, an outdoor heat exchanger functions as the condenser, and an indoor heat exchanger functions as the evaporator. On the other hand, in the heating mode of the air conditioner, the outdoor heat exchanger functions as the evaporator, and the indoor heat exchanger functions as the condenser.
In the cooling mode, the air conditioner allows indoor air to pass through the indoor heat exchanger functioning as the evaporator, thereby discharging cold air to the room. In the heating mode, the air conditioner allows indoor air to pass through the indoor heat exchanger functioning as the condenser, thereby discharging warm air to the room.
A recently developed air conditioner employs an inverter-type compressor which can variably change its refrigerant compression capacity in accordance with a cooling or heating load in a room. Accordingly, it is possible to properly cope with the variation of the cooling or heating load, thereby optimizing the cooling or heating efficiency of the air conditioner.
Generally, a capillary tube or an electronic expansion valve may be used as the expansion device. The electronic expansion valve is mainly used as the expansion device for adjusting the flow rate of the refrigerant so that the cooling or heating capacity of the air conditioner can be variably changed.
The opening degree of a passage in the electronic expansion valve, through which the refrigerant passes, is controlled by a step motor.
Hereinafter, the operation of the above-described conventional controller in a cooling mode will be described in detail.
First, the compressor is operated in accordance with a cooling or heating load in a room, and then the refrigerant circulates through the compressor, the outdoor heat exchanger (functioning as a condenser), the electronic expansion valve, and the indoor heat exchanger (functioning as an evaporator), sequentially. Here, the electronic expansion valve in a closed state is controlled to be opened by a suitable opening degree.
In case that the cooling or heating load in the room is eliminated by the circulation of the refrigerant generated by the operation of the compressor, the compressor is stopped.
In this case, since the pressure at an outlet of the compressor is higher than the pressure at an inlet of the compressor, the refrigerant in a gaseous state flows from the outlet of the compressor to the inlet of the compressor as time goes by. That is, the refrigerant at the outlet of the compressor flows toward the outdoor heat exchanger, the electronic expansion valve, the indoor heat exchanger, and then the inlet of the compressor, thereby achieving the pressure equilibrium between the inlet and outlet of the compressor.
Particularly, in order to more rapidly achieve the pressure equilibrium between the inlet and outlet of the compressor by allowing the refrigerant in a high-pressure state at the outlet of the compressor to flow toward the inlet of the compressor through the electronic expansion valve, the electronic expansion valve is controlled to be completely opened by a constant opening degree.
Thereafter, in case that the compressor is re-operated under the condition in which the cooling or heating load is reduced according to the stoppage of the compressor, the electronic expansion valve is controlled to be closed again, and then to be opened again by the suitable opening degree.
Accordingly, a cooling or heating cycle is obtained by the circulation of the refrigerant of the compressor, thus performing a cooling or heating function.
In order to shorten a time taken to achieve the pressure equilibrium between the inlet and outlet of the compressor, the electronic expansion valve of the above conventional air conditioner must be controlled to be completely opened by the constant opening degree before the compressor is re-operated, and then to be closed after the compressor is re-operated. Thereby, a time taken to control the opening and closing of the passage of the electronic expansion valve is lengthened, thus causing a time taken to re-operate the compressor to be lengthened. Further, the opening degree of the electronic expansion valve is controlled by the step motor, thus causing noise for a comparatively long period of time.